1. Field of the Invention
The present invention is related to apparatus and methods for forming a window in wellbore tubulars, more specifically the invention is related to forming a window in casing and drilling a lateral wellbore in a single trip.
2. Background of the Related Art
The practice of producing oil from multiple, radially dispersed reservoirs through a single primary wellbore has increased dramatically in recent years. Technology has developed that allows an operator to drill a vertical well and then continue drilling one or more angled or horizontal holes off of that well at chosen depth(s). Because the initial vertical wellbore is often cased with a string of tubular casing, an opening or xe2x80x9cwindowxe2x80x9d must be cut in the casing before drilling the lateral wellbore. The windows are usually cut using various types of milling devices and one or more xe2x80x9ctripsxe2x80x9d into the primary wellbore is needed. Rig time is very expensive and multiple trips take time and add to the risk that problems will occur.
In certain multi-trip operations, an anchor, slip mechanism, or an anchor-packer is set in a wellbore at a desired location. This device acts as an anchor against which tools above it may be urged to activate different tool functions. The device typically has a key or other orientation indicating member. The device""s orientation is checked by running a tool such as a gyroscope indicator or measuring-while-drilling device into the wellbore. A whipstock-mill combination tool is then run into the wellbore by first properly orienting a stinger at the bottom of the tool with respect to a concave face of the tool""s whipstock. Splined connections between a stinger and the tool body facilitate correct stinger orientation. A starting mill is releasably secured at the top of the whipstock, e.g. with a shearable setting stud and nut connected to a pilot lug on the whipstock. The tool is then lowered into the wellbore so that the anchor device or packer engages the stinger and the tool is oriented. Slips extend from the stinger and engage the side of the wellbore to prevent movement of the tool in the wellbore; and locking apparatus locks the stinger in a packer when a packer is used. Pulling on the tool then shears the setting stud, freeing the starting mill from the tool. Certain whipstocks are also thereby freed so that an upper concave portion thereof pivots and moves to rest against a tubular or an interior surface of a wellbore. Rotation of the string with the starting mill rotates the mill. The starting mill has a tapered portion which is slowly lowered to contact a pilot lug on the concave face of the whipstock. This forces the starting mill into the casing and the casing is milled as the pilot lug is milled off. The starting mill moves downwardly while contacting the pilot lug or the concave portion and cuts an initial window in the casing. The starting mill is then removed from the wellbore. A window mill, e.g. on a flexible joint of drill pipe, is lowered into the wellbore and rotated to mill down from the initial window formed by the starting mill. The tool is then removed from the wellbore and a drill string is utilized with a drill bit to form the lateral borehole in the formation adjacent the window. There has long been a need for efficient and effective wellbore casing window methods and tools useful in such methods particularly for drilling side or lateral wellbores. There has also long been a need for an effective xe2x80x9csingle tripxe2x80x9d method for forming a window in wellbore casing whereby a window is formed and the lateral wellbore is drilled in a single trip.
There is a need therefore, for a window forming apparatus that includes fewer mechanical components. There is a further need for a window forming apparatus that requires fewer trips into a wellbore to complete formation of a window in casing.
The present invention discloses and claims methods and apparatus for forming an opening or a window in a downhole tubular for the subsequent formation of a lateral wellbore. In one aspect of the invention, a container having an exothermic material is lowered into a wellbore to a predetermined depth. Thereafter, the exothermic material is ignited and a portion of the casing therearound is destroyed, leaving a window in the casing. In another aspect of the invention, the apparatus includes a run-in string or drill stem with a drill bit attached to a lower end thereof. A diverter, like a whipstock is attached temporarily to the drill bit with a mechanically shearable connection. At a lower end of the whipstock, a container is formed and connected thereto. The container is designed to house a predetermined amount of exothermic material at one side thereof adjacent the area of casing where the window or opening will be formed. A telescopic joint extends between the bottom of the container and an anchor therebelow and the telescopic joint is in an extended position when the apparatus is run into a wellbore.
In an aspect of the invention, the window is formed in the casing by first locating the apparatus in a predetermined location in the wellbore and setting the anchor therein. Subsequently, a thermite initiator is activated, typically by a hydraulic line between the initiator and hydraulic ports formed in the drill bit. The initiator activates a thermite fuse and the chemical process within the package of thermite begins producing heat for a given amount of time adequate to form the window or hole in the adjacent casing. As the thermite burns, the melted casing and thermite material is urged into the container by formations formed at the upper and lower edges of the container. As the thermite completes its burning process, a telescopic joint fuse connected between the lower portion of the thermite package and the telescopic joint is activated and the telescopic joint, having an atmospheric chamber formed therein, begins to retract. As the joint retracts, the shearable connection between the drill and whipstock fails and the container and whipstock move downward to a predetermined, second axial position within the wellbore. In the second position, the whipstock is properly placed to guide the drill bit through the newly formed window in the casing. As the container moves downward, the formations at the upper and lower edge remove any slag from the inside perimeter of the newly formed window. With the whipstock physically separated from the drill stem and drill bit and the whipstock properly located and anchored in a position appropriate for formation of the lateral wellbore, the drill stem and rotating drill bit are extended to form the lateral welbbore.